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Freak waves prove to be ultimate icebreaker

Scientists from the National Institute of Water and Atmospheric Research (Niwa) found that waves bigger than 3 metres break ice much further away from the sea-ice edge than previously thought. Niwa oceanographer Dr Mike Williams said the study, published in Nature today, provided vital information that had been missing from models of sea ice and its effect on climate.

''When these experiments were last carried out in the 1970s and 80s, people needed to be sitting on the sea ice to take measurements and that meant they couldn't be out there when the big waves came through,'' Williams said.

The Niwa team developed wave buoys, so they ''were able to put those out on the ice and leave them out during big storms'', he said.

Niwa hydrodynamics scientist Dr Alison Kohout deployed the buoys from the Aurora Australis, the Australian icebreaker used to free a Russian ship trapped in Antarctic ice for 10 days over summer.

The Niwa scientists also compared data from 1997 to 2009 to examine the link between wave heights in the Southern Ocean and sea ice extent.

''What we've found is that where waves have got bigger the sea ice has retreated, and where waves have got smaller the sea ice has expanded,'' Williams said.

The research helped to explain why Antarctic sea ice had been increasing in some areas where climate models predicted it would decrease.

The effect of waves on sea ice has been known since the early days of Antarctic exploration. Ernest Shackleton was ''famous for having had his ship trapped in ice'', Williams said.

After the men abandoned ship in the Weddell Sea, ''freak waves'' broke up the ice they had sought safety on.

Williams said the knowledge could be beneficial for ships that get stuck in sea ice, if they knew there were big waves coming that could break the ice around them. He said understanding how sea ice expands and retracts was an imdhportant part of climate modelling.